Pharmaceuticals having an optical isomer are required to be produced as optically pure compounds in view of side effects, for example. Therefore, optical resolution and optical purity test have become increasingly important. In particular, since optically active amines such as ethanolamine derivatives and catecholamine derivatives have physiological activities on the central nervous system, they are important compounds as intermediates for various pharmaceuticals. Moreover, natural amino acids and physiologically active substances are all chiral compounds. Thus, research on a variety of chiral sensors has been conducted for optical resolution and analytical purposes of the optically active amines.
The inventors previously have found out that optically active pseudo-18-crown-6 having a variety of metacyclophane structures, for example, have high asymmetry recognition ability toward primary amines (see Japanese Laid-Open Patent Publication No. 2004-75624).
For example, a selector that is represented by the following formula and in which pseudo-18-crown-6 is bound to a silica gel is applied to column chromatography and shows excellent separation ability toward a variety of primary amines.

Moreover, the pseudo-18-crown-6 that is represented by the following formula and into which a 2,4-dinitrophenylazo group, which is a chromophore, is introduced changes its absorption spectrum significantly by forming a complex with an amine. As a result, the color is changed to such an extent that the change can be observed visually, so that this pseudo-18-crown-6 can be used as a chiral indicator. However, this pseudo-18-crown-6 is still not sufficient as a chiral sensor in view of the detection sensitivity.

Chemical sensors such as chiral sensors are devices having a receptor site that recognizes a specific ion or molecule as a target and is bound thereto, and these devices read a change in the electronic state resulting from the binding to the target as an optical response (e.g., a change in absorption or fluorescence spectrum) or an electrical response (e.g., a change in electrical conductivity or oxidation-reduction potential). The sensitivity of the chemical sensors depends on the degree of binding ability between the target and the receptor site (complex stability constant) and the efficiency of converting the changes in the electronic state of a sensor molecule into signals. This will be described on the basis of the following scheme:

As shown in (A) of the scheme, usually, a signal is generated in one-to-one correspondence with a binding between the target and the receptor site. In order to increase the detection sensitivity, it is necessary to increase the complex stability constant so as to increase the number of targets to be bound, but the selectivity decreases. On the other hand, if a highly configured receptor site is used in order to improve the selectivity, then the complex forming rate is reduced, and thus a response cannot be provided quickly. To address this problem, a molecular wire method, which is a method for achieving a high sensitivity by increasing the signal conversion efficiency using a conjugated polymer, has been proposed ((B) of the scheme; see T. M. Swager, Acc. Chem. Res., vol. 31, p. 201, 1998; and Ichiro Ohki and Yoshito Tobe, Chemistry, vol. 56, p. 62, 2001).
When a conjugated polymer is used as in (B) of the scheme, receptor sites can be immobilized to a carrier, and furthermore electrons and holes or the excitation energy can move freely within an effective conjugated chain. For example, when the target is bound to any given portion of the receptor sites of a conductive polymer, the electronic state of the effective conjugated chain is changed, which results in a change in the electrical conductivity or the oxidation-reduction potential of the polymer (see (B) of the scheme). In the case of a fluorescent polymer, the excitation energy that moves in the conjugated chain is deactivated by the target bound to one receptor site, which results in a quenching of the fluorescence due to the polymer. In other words, whichever receptor site within the effective conjugated chain the target is bound to, an electrical or optical response can be obtained, so that a high sensitivity that conventional low molecular weight sensors have not provided can be achieved. Specifically, poly(p-phenylene ethynylene) or polythiophene having conductivity and strong fluorescence emission properties is used for the polymer main chain, and a host molecular framework such as electron-donative cyclophane or calixarene is used for the receptor site (see Q. Zhou and T. M. Swager, J. Am. Chem. Soc., vol. 117, p. 7017, 1995; Q. Zhou and T. M. Swager, J. Am. Chem. Soc., vol. 117, p. 12593, 1995; K. B. Crawford et al., J. Am. Chem. Soc., vol. 120, p. 5187, 1998; J.-S. Yang and T. M. Swager, J. Am. Chem. Soc., vol. 120, p. 5321, 1998; J.-S. Yang and T. M. Swager, J. Am. Chem. Soc., vol. 120, p. 11864, 1998; and J. Kim et al., Angew. Chem. Int. Ed., vol. 39, p. 3868, 2000).